1. Field of the Invention
This invention relates to radio telephones and base stations for such radio telephones and to a method of communication in radio telephone systems.
2. Description of the Prior Art
One type of radio telephone system to which the invention relates is DECT (Digital European Cordless Telecommunications). A DECT system typically includes at least one fixed part, comprising one or more base stations, and several portable parts, or handsets. The handsets communicate with a base station using an over the air radio carrier which is divided into time slots. The base station may be connected to a standard wireline telephone system and the handsets may then communicate with the wireline system through the base station. The handsets may also communicate with each other through the base station. Most communication between the base station and a handset requires a communication linkxe2x80x94that is a link for bi-directional communication between the base station and the handset. Each communication link uses two time slots, one for communications from the base station to the handset and one for communications in the opposite direction.
When an incoming telephone call is received by the base station (for example from the wireline system or from one of the handsets of the radio telephone system to another) and is to be directed to a single one of the handsets a standard protocol is used to establish a communication link between the base station and the handset. The base station first issues a broadcast (xe2x80x9cB-formatxe2x80x9d) paging signal whose contents specify the handset to be called. In response to this the handset specified in the signal establishes a bi-directional point-to-point communication link with the base station by replying with an xe2x80x9cS-formatxe2x80x9d {LCE-PAGE-RESPONSE} signal; the incoming call is routed to that link via a {CC-SETUP} message; the handset and the base station negotiate the communication format to be used over the link; the handset then alerts its user (for example by ringing, or flashing an LED, or by other alerting means); the handset transmits a {CC-ALERTING} signal to the base station; and if the user answers the call (for example by pressing a key on a keypad of the handset) the handset transmits a {CC-CONNECT} signal to the base station, the base station answers with a {CC-SETUP-ACK} signal and the voice (or data) signal of the incoming call is connected over the link to the handset. The handset may be configured to answer the call automatically so that the user does not need to press a key.
If an incoming call is not to be directed to a single one of the handsets it can be useful for as many of the handsets as possible to be alerted to the call so that a user of any of those handsets may answer it. One way to achieve this is with a similar system to the one described abovexe2x80x94that is to use one paging signal directed specifically to each individual handset to inform each handset of the call. However, this requires a communication link using two communication slots for each handset that is to ring, and the number of slots is limited. Therefore, in a system with numerous handsets it may not be possible to establish a communication link with every handset simultaneously. For instance, in a DECT system with 24 available slots no more than 12 handsets could be alerted simultaneously in this way.
According to a first aspect of the present invention there is provided a base station for a DECT-like radio telephone system comprising at least one handset, the base station comprising base station communication means for transmitting signals to the handset; and base station processing means responsive to an incoming call to the base station for causing the base station communication means to transmit a signal analogous to an {LCE-PAGE-REQUEST} signal of a type that specifies no single handset.
According to a second aspect of the present invention there is provided a handset for a DECT-like radio telephone system comprising a base station, the handset comprising handset communication means for receiving signals from the base station; alerting means; and handset processing means responsive to the handset communication means receiving a signal analogous to an {LCE-PAGE-REQUEST} signal of a type that specifies no single handset for activating the alerting means.
The system preferably includes more than one handset. The communication means of the base station and of the handsets preferably each include an antenna and a transceiver connected to the respective processing means. Preferably both a base station and a handset according to the invention are provided.
Preferably, the base station processing means is responsive to a signal from a first handset requesting a call to be set up while the incoming call remains unanswered for causing the base station to route the call to the first handset. Preferably, the base station processing means is responsive to a subsequent signal from a second handset requesting a call to be set up for causing the base station communication means to transmit a signal to reject the request from the second handset
The signal requesting a call to be set up is suitably a signal for establishing bi-directional communication with the base station, for example a signal conventionally used for that function such as a signal analogous to an {LCE-PAGE-RESPONSE} signal. Preferably, this is a point-to-point xe2x80x9cS-formatxe2x80x9d signal.
The signal analogous to an {LCE-PAGE-REQUEST} signal of a type that specifies no single handset suitably has first and second type digits which are both hexadecimal F. Suitably the seventh least significant TPUI bit of that signal is 1. Suitably the four least significant TPUI bits of the signal specify an alerting type to be used by the handset. Preferably, the base station transmits the signal as a broadcast (xe2x80x9cB-formatxe2x80x9d) signal. Preferably, a DLC (Data Link Control) link between the base station and the handset is unnecessary for the base station communication means to transmit the signal.
The base station processing means is preferably responsive to the incoming call being released for causing the base station communication means to transmit a signal indicating that the call has been released. That signal preferably specifies no single handset.
Signals that specify no single handset preferably specify no handset or group of handsets. Any portions of those signals conventionally used to specify a handset or group of handsets are preferably used for another function, most preferably to specify the action to be taken by handset processing means on receipt of the signals by handset communication means.
The handset processing means is preferably responsive to the handset communication means receiving a signal analogous to an {LCE-PAGE-REQUEST} signal of a type that specifies no single handset, and that has at least one TPUI bit specifying that the alerting means is to be deactivated, for deactivating the alerting means.
According to a third aspect of the invention there is provided a method for communication between a base station and a handset in a DECT-like radio telephone system, the method comprising:
in response to an incoming call to the base station, transmitting from communication means of the base station a signal analogous to an {LCE-PAGE-REQUEST} signal of a type that specifies no single handset; and
in response to communication means of the handset receiving that signal, activating alerting means of the handset.
The term xe2x80x98DECT-like radio telephone systemxe2x80x99 includes any radio telephone system that uses an analogous communication protocol to that of the DECT system, irrespective of the terminology applied to the system""s signalling. This includes the DECT system itself, WCPE (Wireless Customer Premises Equipment), PHS (Personal Handyphone System) and DCT900. The term xe2x80x98signal analogous to an {LCE-PAGE-REQUEST} signalxe2x80x99 includes DECT""s {LCE-PAGE-REQUEST} signals and signals of DECT-like radio telephone systems having functions analogous to those of the {LCE-PAGE-REQUEST} signal in a DECT system. Similarly, the term xe2x80x98signal analogous to a {CC-SETUP} signalxe2x80x99 includes DECT""s {CC-SETUP} signals and signals of DECT-like radio telephone systems having functions analogous to those of the {CC-SETUP} signal in a DECT system.